"My prayers go out to all the people in Boston, and I want to commend them for the way they've stuck together and the unity they've shown during this time," LL said. "It's just proof of how important it is for us as Americans to get along and to really come together as one."

Heaton also shared her feelings on the tragedy and reflected on one poignant moment. "When I saw the picture of the young boy -- the eight-year-old who was killed -- I think it was his first Communion picture, it really broke my heart," she said. "That poor family took so much loss, I really pray for them."

The Bible star Roma Downey, who attended the event with her producer husband Mark Burnett, said she feels it's important to focus on the people making a positive impact in the wake of such tragedies. "We need to remember there are good people doing good things, and we need to make a lot of noise for the good guys."

Watch the video to learn more about why the celebrities are lending their support to Mattel Children's Hospital UCLA, which aims to provide a better future for sick children through innovative research, new approaches to delivering care and education programs for the next generation of physicians and scientists.